JP11-201211A, published by the Japan Patent Office in 1999, discloses an attachment structure for a base valve which is fixed into position on a lower cap of a double tube hydraulic shock absorber. As shown in FIG. 3, a lower cap 34 is fitted into a base end of an outer tube 32 and welded thereto at its outer periphery such that the base end of the outer tube 32 is blocked in an oil tight fashion. A base valve 35, which is fitted and fixed to a base end of an inner tube 33, is fixed into position on an upper surface of the lower cap 34.
The base valve 35 comprises a valve case 36, a non-return valve 37, a pressure side damping force-generating valve 38, and a fixing pin 39. The valve case 36 comprises a pressure side port 36a and an expansion side port 36b. The non-return valve 37 is disposed on an upper surface of the valve case 36 so as to cover the expansion side port 36b openably. The pressure side damping force-generating valve. 38 is disposed on a lower surface of the valve case 36 so as to cover the pressure side port 36a openably. The fixing pin 39 fixes the non-return valve 37 and pressure side damping force-generating valve 38 to the valve case 36 by means of pressure.
A plurality of leg portions 40 contacting the upper surface of the lower cap 34 are formed on a lower surface outer peripheral portion of the valve case 36 so as to protrude at predetermined intervals on the circumference. Oil passages are provided between adjacent leg portions 40, and these oil passages communicate with a reservoir chamber 42 formed between the inner tube 33 and outer tube 32.
During a compression operation of the double tube hydraulic shock absorber, a piston rod 41 penetrates the inner tube 33, creating surplus operating fluid in an amount corresponding to the volume of the penetrating rod. This surplus operating fluid is delivered to the reservoir chamber 42 via the pressure side port 36a, the pressure side damping force-generating valve 38, and the aforementioned oil passages, and thus a predetermined pressure side damping force is generated by the pressure side damping force-generating valve 38.